Electric motor.



B. BRETCH.

ELECTRIC MOTOR.

APPLICATION FILED JULY 31, 1908.

Patented Oct. 15, 1912.

Inventor: Edward Evretch bY AbTY's.

UNITED STATES PATENT OFFICE.

EDWARD BRETCI-I, OF ST. LOUIS, MISSOURI.

ELECTRIC MOTOR.

To all whom it may concern:

Be it known that I, EDWARD Bua'rcir, a citizen of the United States,residing at St. Louis, Missouri, have invented a certain new and usefulImprovement in Electric Motors, of which the following is a full, clear,and exact description, such as will enable others skilled in the arttowhich it appertains to make and use the same, reference being had to theaccompanying drawings, forming part of this specification, in whichFigure 1 is a front elevational view of a motor constructed inaccordance with my invention; Fig. 2 is a sectional view takenapproximately on the line 2-2 of Fig. 1; Fig. 3 is a diagrammatical viewof the armature and field. Fig. 4 is an elevation of one of the armaturedisks and showing the slots therein.

This invention relates to electric motors, and more particularly toalternating current induction motors in which there is no commutator,the armature circuits being permanently closed.

One of the objects of my invention is to provide a single phaseinduction motor which will be inherently self starting, the same aspolyphase motors.

Another object is to provide an induction motor which is so constructedthat the noise peculiar to this class of motors is eliminated.

Other objects and advantages as well as the novel details ofconstruction will be hereinafter more fully described and pointed out inthe claims.

In the drawings, 1 indicates a motor housing provided with bearingswithin which an armature shaft 2 is mounted. The same general style ofarmature that is used with polyphase motors can be used in connectionwith my invention, the squirrel cage type being preferred especially insmall size motors. The armature shown in Figs. 1, 2 and 3 consists ofthe usual laminated structure 3 secured to the shaft 2 and conductingend rings 4. Conductors 5 are arranged in slots in the laminatedstructure and have their ends bent around flanges 4 on the end rings andsoldered thereto. This armature construction possesses both simplicityand mechanical strength as no holes are required in the end rings forscrewing or riveting the conductors thereto and said conductors firmlyclamp the laminated structure together.

Specification of Letters latent.

Application filed July 31, 1908.

Patented Oct. 15, 1912. Serial No. 446,260.

Fig. 4 illustrates a modified form of armature in which the flanges onthe end rings are dispensed with, the ends of conductors 5" being bentinwardly against the outer face of the rings 4.

The field shown in Fig. l and Fig. 3 is of the four pole type andcomprises a laminated structure built 11 of punchings, having teeth 6which receive the winding. In winding each pole of this field aconductor is first wound around one tooth the required number of turnsand then wound to include both the first tooth and the next adjacenttooth and thereafter wound to include the first three teeth, and so onuntil the required number of teeth for the pole are included, as showndiagrammatically in Fig. 3. Under certain conditions it is desirable toinclude more than one tooth in the first coil, the object being toproduce a field pole in which the flux diminishes to zero more abruptlyon one side of the point of maximum density thanon the other. A shortcircuited conductor in an alternating field tends to move entirely outof it or into a weaker field, and as in the usual alternating currentfield winding there are an equal number of armature conductors under apole on each side of the point of maximum flux density the forces justbalance at standstill. If the field is wound as shown diagrammaticallyin Fig. 3, making one side of the pole the strongest instead of themiddle as is usually done, and gradually tapering the strength from oneside of the pole to the other, the forces acting on the short circuitedconductors of the armature are no longer balanced but have a tendency tomove the conductors from the strong side of the pole to the weaker, andby arranging the pole strength to taper the same way in all the polesaround the field the motor becomes self starting with the same generalcharacteristics as the ordinary two and three phase motors. Whilearranging the windings to make one side of the pole the position ofmaximum strength may give the greatest starting torque, it isnevertheless evident that if the maximum strength is displaced to oneside of the middle of the pole, even though it is not at the extremeedge, or if only a part of the poles are wound to produce adisplacement, the motor will be self starting, the degree of startingtorque varying with the construction and effectiveness of the fluxdisplacement.

In order to eliminate the noise peculiar to induction motors I constructmy improved motor so that the number of conductor receiving slots in thefield and armature have for a common divisor a number the same as thenumber of poles; for example, as shown in Fig. 3 in which a four polemotor is provided with a field having twenty-four wire receiving slotsand an armature having twenty slots. In the usual construction whereinthe number of slots or teeth in the field and armature have no commondivisor the forces acting between the field and armature are never thesame in all the poles at any instant since the relation between theconductors of the field and armature cannot be the same in all the polesat any instant. The consequence is that these unbalanced forces varyingfrom instant to instant set up vibration in the motor which produces anoise. lVhen constructed so that the teeth of each member have a commondivisor equal to the number of poles, any pole of the armature bears thesame relation to the corresponding pole of the field as any other andthe result is a perfect balance of all forces in any position, thuseliminating the vibration.

\Vhile a form of squirrel cage armature is described in connection withmy improved motor, any of the usual formsof armature used in polyphasemotors may be used in lieu thereof. In case it is necessary to hold downthe starting current under severe starting conditions, or on someclasses of variable speed work, a form of armature in which resistancecan be inserted may be used. The speed may be varied by supplying thefield with reduced voltage by a rheostat or transformer. The number ofpoles and the number of teeth per pole may also be varied to suitvarious condiions.

In Fig. 3 I have shown a regularly spaced field punching such as is usedin the ordinary polyphase motors having some of the teeth cut away toaccommodate the comparatively large number of conductors along one sideof the poles.

Where I use the term field in the claims it is to be understood as theprimary member, and armature the secondary member, regardless of whichmay be the movable member, and by the term alternating current I mean toinclude any current which varies in intensity and is capable ofproducing an inductive efl'ect on a secondary winding irrespective ofwave form.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. An electric motor having a field, an armature, conductors in the formof bars extending across said armature, a flanged conductor forelectrically connecting said bars, the ends of said bars being bent intointerlocking engagement with the flange of said conductor; substantiallyas described.

2. An electric motor having a field, an armature, conductors in the formof bars extending across said armature, a flanged conductor forelectrically connecting said bars, said bars being mechanicallyconnected to said conductor by having their end portionsinterlocked withthe flange on the conductor; substantially as described.

3. An electric motor having a field, an armature provided with alaminated core, conductors in the form of bars embedded in the surfaceof the armature and extending across the same, conducting rings on theends of the armature, flanges on said conducting rings, and the endportions of said bars being bent around said flanges; substantially asdescribed.

4. An electric motor having a field, an armature provided with alaminated core, conductors in the form of bars embedded in and extendingacross the armature core, a flanged conducting ring arranged on eachside of the armature core, the end portions of said bars being bentaround the edges of said rings; substantially as described.

In testimony whereof I hereunto affix my signature in the presence oftwo witnesses, this twenty seventh day of July 1908.

EDWARD BRETCH.

GEORGE BAKEwELL.

